Lithium aluminum complex hydroxide salts expressed by the following formula,[Al2Li(OH)6]2.A.mH2O                wherein A is a divalent anion,have heretofore been known, and those in which the divalent anion A is a carbonate anion (CO32−) or a silicate anion (Si3O72−) have been used being mixed as heat retaining agents into the films for agricultural use (see patent documents 1 and 2).        
Patent document 1: JP-A-7-286052
Patent document 2: Japanese Patent No. 2852563